Eight Republican candidates are lining up for the first in a series of debates that will help define the party's nomination battle to take on Barack Obama next year for the White House.

The main focus of Wednesday night's debate at the Ronald Reagan Library in the Simi Valley, near Los Angeles, will be on whether Texas governor Rick Perry, who only entered the race last month, can consolidate his frontrunner status.

Tom Mann, a political analyst at the Brookings Institution, said: "It is interesting because of Rick Perry, and the fact that he has sky-rocketed to the lead in the Republican field without many people having a firm hold on him, just some impressions."

In spite of eight candidates sharing the platform in the debate, the nomination is already shaping up as a two-horse race between Perry and Mitt Romney, according to the polls, with Michele Bachmann trailing in third place along with outsider Ron Paul.

Mann said Perry's record of speeches and writing leaves him vulnerable. He said: "The question is whether Romney can show some signs of life and put himself back into the thick of the race. Everything else is beside the point. There are no other plausible candidates for the nomination. The others are just window-dressing on the side."

Job creation will be one of the dominant issues in the debate, which comes the day before Obama's speech on Thursday to a joint session of Congress in which he will propose a job stimulus package that that will cost $300bn to cut taxes, help state governments and pay for the building or rebuilding of roads, bridges and other infrastructure projects.

To appease Republicans, Obama will propose the $300bn in spending will be matched by $300bn in cuts elsewhere.

Perry received a pre-debate boost this morning when the Wall Street Journal, whose opinion pages remain a bastion of conservatism, offered a damning verdict on a jobs plan put forward on Tuesday by Romney, a relative moderate compared with almost all of his rivals.

The Journal, in an editorial, described Romney's 59-point jobs plan, which proposes modest tax cuts and a reduction in federal government regulations, as "surprisingly timid and tactical considering our economic predicament", and lambasted him for proposing a trade war with China.

It added: "The biggest rap on Mr Romney as a potential president is that it's hard to discern any core beliefs beyond faith in his own managerial expertise."

The Journal editorial followed criticism by Perry's campaign of the Romney plan. Perry's team said Romney, while governor of Massachusetts, failed to put into practice many of the reforms he now claims to support.

Wednesday's debate kicks off months of intensive campaigning, with the candidates making frequent trips to Iowa, New Hampshire, Nevada and South Carolina, the states scheduled to hold the first of the nomination caucuses and primaries in February.

Perry's rapid rise would be halted if he comes across in the debate as too smug, or if his Texas accent reminds voters too much of George Bush, or if he makes a gaffe, as he did last month when suggesting that the chairman of the Federal Reserve, Ben Bernanke, would be treated "pretty ugly" if he came to Texas, or even his hint in 2009 that he supported Texas seceding from the union.

Political analysts such as Norm Ornstein, a non-partisan commentator who works at the rightwing thinktank the American Enterprise Institute, note that Perry is also vulnerable on policy issues such as social security.

Perry recently reassured those receiving social security that if he were president their benefits would be safe, but in one of his books he described social security as unconstitutional.

Ornstein said Perry's rivals in the debate should be asking him: 'Were you lying then or are you lying now?'

The dilemma for Perry's opponents is whether to direct their attacks at him tonight or hold off until later. Personal attacks can backfire, as they did for the former governor of Minnesota, Tim Pawlenty, during the last debate when he turned on Bachmann in a desperate attempt to grab attention. Bachmann won the Republican straw poll in Ames, Iowa, two days later, with Pawlenty performing badly and dropping out of the race.

The victory in the Ames poll has been the high point for Bachmann, who has since seen a slump in her fortunes, mainly because of the entry of Perry, who appeals to the same rightwing vote.

Others in the debate are businessman Herman Cain, former House Speaker Newt Gingrich, former ambassador to China Jon Huntsman and former senator Rick Santorum, all languishing in single figures in the polls, with little chance of winning the nomination.

This is the first of at least six debates this autumn, with the next scheduled for Monday in Tampa, Florida.